And I'm Melissa Block. We begin this hour with the horrific story unfolding today out of Boston. Just over four hours into the Boston Marathon, two explosions ripped into a crowd of onlookers and runners not far from the finish line. Boston Police have confirmed at least two people dead, and 23 injured. Massachusetts Gov. Deval Patrick spoke just moments ago, along with the city's police commissioner, Ed Davis.

GOV. DEVAL PATRICK: At 2:50 p.m. today, there were simultaneous explosions that occurred along the route of the Boston Marathon, near the finish line. These explosions occurred 50 to 100 yards apart, and each scene resulted in multiple casualties.

BLOCK: For more, we're joined by NPR's Tovia Smith in Boston. And Tovia, what more have you learned?

TOVIA SMITH, BYLINE: Well, as the governor himself put it just a few minutes ago, we do not have the full picture yet. When asked specifically if this was a terrorist attack, the Boston police commissioner responded, "you can reach your own conclusions." Besides the two explosions on Boylston Street that came just seconds apart - just before 3 o'clock, near the finish line - there's been another blast since. That was a controlled explosion of a suspicious package.

But there was also another explosion - not on purpose, not controlled by police or authorities; but that was at the JFK Library, which is not nearby. It's across town. That was another explosive device. Police are asking anybody with any information about any of it to give them a call to the tip line, and they are investigating.

BLOCK: I'm also seeing alerts from the Boston Police Department, asking people not to congregate in large crowds. I assume they are looking for any other suspicious packages in a very - it sounds like what must be a very broad area, at this point.

SMITH: That's right. They're telling everybody, stay home. If you're in hotels in the area - which, of course, there are many, many people; thousands and tens of thousands - they say, don't come out of your room. Don't go anywhere. Don't congregate.

They say that many people who were running away from the scene dropped bags, and all of those are being treated as suspicious. You can only imagine how many there are on the sidewalk, down in that area. And they are not giving anything like an all-clear at this point. It is a very volatile situation and still a dangerous one.

BLOCK: And Tovia, some awful, awful images of the casualties from these explosions. What else can you tell us about the injured and their condition?

SMITH: The governor called it a horrific day. There were at least two confirmed deaths, we know already. The images from the area - we saw people being pulled away on gurneys, and wheeled away on wheelchairs. There was blood staining the sidewalk in the area, shattered glass of buildings around; the grandstands that were set up for - at the finish line collapsed to the ground.

When the explosion hit, there was gray smoke that filled up in the air. You could see there were cameras everywhere - obviously - for the race. We saw that smoke go up. We see the dust on the ground now. Streets that were packed only a few hours ago, are now absolutely empty except for law enforcement.